Polycarbonates are well known amorphous polymers known inter alia for their transparency, toughness and impact resistance. However in order to stabilize polycarbonates or provide or enhance certain characteristics which are not inherently present or only present to a slight extent in polycarbonates, additive addition is employed. Non limiting examples of such additives include thermal stabilizers such as phosphites, stabilizers against ultraviolet radiation effects such as the benzophenones or benzotriazoles, mold release additives, fillers such as fibers or mats preferably glass fibers, flame retardant materials such as halogen substituted organics and salts, particularly aryl sulfonate salts, and the like. One of the positive attributes an additive must have is compatibility with the resin particularly at the processing temperatures of the additive containing composition. Sometimes the processing temperature of the polymer containing composition is so high a particular additive therein is substantially volatilized, substantially degraded, or interacts with the polymer. Such degradation of the additive can also lead to degradation of the polymer itself. Whatever the mechanism of action, it has been found that certain additives which perform up to expectations in certain polymer systems do not perform well in other polymer systems.
One of the potential problems in processing aromatic polycarbonates has been caused by its high Tg. Although this is partially responsible for certain of its excellent properties, care must be taken to avoid thermal damage to the aromatic polycarbonate whereby its properties are lessened through thermal degradation of the polymer per se or additives which may be present. It is also possible to remove certain classes of potential additives as effective aromatic polycarbonate additives due to their lack of stability, volatility or in general their response to the thermal processing window.
Recently, a new copolyestercarbonate has been prepared. This new polymer described in U.S. Pat. No. 4,983,706 as well as U.S. patent Ser. Nos. 07/455,118, 07/476,068 and 07/627/517 has aromatic polycarbonate like properties together with substantially increased flow at the same molecular weight as an ordinary aromatic polycarbonate. Moreover, it can be processed at a significantly reduced temperature than an aromatic polycarbonate having substantially the same properties because of a reduced Tg. This polymer system is a species of a broader class of polymer composition which have polycarbonate or polycarbonate like properties but which can be processed at significantly lower temperatures. These polycarbonate or polycarbonate like compositions can have admixed therein additives which previously could not be processed compatibly with the traditional aromatic polycarbonates such as bisphenol-A polycarbonate. Examples of such polycarbonate polymer systems having significantly reduced processing temperatures include but are not limited to the following: polycarbonates with plasticizers such as a phosphate, polycarbonates with long chain aliphatic carboxylic chain stoppers, polycarbonates with short chain aliphatic carbonates, oligomeric carbonates, polycarbonates with selected dihydric phenols such as those having a long chain aliphatic group on the gem carbon atom connecting the two phenols. Examples of blends of polycarbonates with other polymers wherein the blend has a significantly lower processing temperature than polycarbonate include admixing polycarbonate with polyesters, such as, polybutylene terephthalate and 1,4-cyclohexanedimethanol containing polyesters.
It has now been discovered that certain additives which were once considered borderline or ineffective with polycarbonate can now be successfully processed with such polycarbonate systems, particularly, an aromatic copolyestercarbonate having polycarbonate like properties described above. Although not to be constrained to this theory of mechanism, it is believed that the lower processing temperature of the new copolyestercarbonate maintains the integrity of the additive during processing. These new compositions are now available for applications which were not filled or inadequately filled by past aromatic polycarbonate compositions.